scholarly journals Line-shape broadening of an autoionizing state in helium at high XUV intensity

2021 ◽  
Author(s):  
Lennart Aufleger ◽  
Patrick Friebel ◽  
Patrick Rupprecht ◽  
Alexander Magunia ◽  
Thomas Ding ◽  
...  
Keyword(s):  
Excited State ◽  
Strong Coupling ◽  
Line Shape ◽  
Transient Absorption ◽  
Extreme Ultraviolet ◽  
Model Simulation ◽  
Transient Absorption Spectroscopy ◽  
Autoionizing State ◽  
Doubly Excited ◽  
Level Model

Abstract We study the interaction of intense extreme ultraviolet (XUV) light with the 2s2p doubly excited state in helium. In addition to previously understood energy-level and phase shifts, high XUV intensities may lead to other absorption line shape distortions. Here, we report on experimental transient-absorption spectroscopy results on the 2s2p line width modification in helium in intense stochastic XUV fields. A few-level model simulation is realized to investigate the origins of this effect. We find that the line shape broadening is connected to the strong coupling of the ground state to the 2s2p doubly excited state which is embedded in the ionization continuum. As the broadening takes place for intensities lower than for other strong-coupling processes, e.g. observing asymmetry changes of the absorption profile, this signature can be identified already in an intermediate intensity regime. These findings are in general relevant for resonant inner shell transitions in nonlinear experiments with XUV and x-ray photon energies at high intensity.

scholarly journals Bound-State Electron Dynamics Driven by Near-Resonantly Detuned Intense and Ultrashort Pulsed XUV Fields

2020 ◽  
Vol 10 (18) ◽  
pp. 6153
Author(s):  
Alexander Magunia ◽  
Lennart Aufleger ◽  
Thomas Ding ◽  
Patrick Rupprecht ◽  
Marc Rebholz ◽  
...  
Keyword(s):  
Numerical Model ◽  
Electric Fields ◽  
Line Shape ◽  
Transient Absorption ◽  
Extreme Ultraviolet ◽  
Analytical Calculation ◽  
Underlying Mechanism ◽  
Bound State ◽  
Transient Absorption Spectrum ◽  
Autoionizing State

We report on numerical results revealing line-shape asymmetry changes of electronic transitions in atoms near-resonantly driven by intense extreme-ultraviolet (XUV) electric fields by monitoring their transient absorption spectrum after transmission through a moderately dense atomic medium. Our numerical model utilizes ultrashort broadband XUV laser pulses varied in their intensity (1014–1015 W/cm2) and detuning nearly out of resonance for a quantitative evaluation of the absorption line-shape asymmetry. It will be shown how transient energy shifts of the bound electronic states can be linked to these asymmetry changes in the case of an ultrashort XUV driving pulse temporally shorter than the lifetime of the resonant excitation, and how the asymmetry can be controlled by the near-resonant detuning of the XUV pulse. In the case of a two-level system, the numerical model is compared to an analytical calculation, which helps to uncover the underlying mechanism for the detuning- and intensity-induced line-shape modification and links it to the generalized Rabi frequency. To further apply the numerical model to recent experimental results of the near-resonant dressing of the 2s2p doubly excited state in helium by an ultrashort XUV free-electron laser pulse we extend the two-level model with an ionization continuum, thereby enabling the description of transmission-type (Fraunhofer-like) transient absorption of a strongly laser-coupled autoionizing state.

Sub-100 Fs Intersystem Crossing to a Metal-Centered Triplet in Ni(II)OEP Observed with M-Edge XANES

2019 ◽  
Author(s):  
Elizabeth S. Ryland ◽  
Kaili Zhang ◽  
Josh Vura-Weis
Keyword(s):  
Excited State ◽  
Time Resolution ◽  
Transient Absorption ◽  
Extreme Ultraviolet ◽  
High Harmonic ◽  
Transient Absorption Spectroscopy ◽  
Intersystem Crossing ◽  
Edge Structure ◽  
State Spin ◽  
X Ray Absorption

Nickel porphyrins have been extenstively studied as photosensitizers due to their long-lived metal-centered excited states. The multiplicity of the (d,d) state, and/or the rate of intersystem crossing between singlet and triplet metal-centered states, has remained uncertain due to the spin-insensitivity of many spectral probes. In this work, we directly probe the metal 3d shell occupation of nickel(II) octaethylporphyrin (NiOEP) using femtosecond M2,3-edge X-ray absorption near-edge structure (XANES). A tabletop high-harmonic source is used to perform 400 nm pump, extreme-ultraviolet probe transient absorption spectroscopy with ~100 fs time resolution. Photoexcitation produces a (π,π*) state that evolves with a time constant of 48 fs to a vibrationally hot metal-centered triplet 3(d,d) excited state with a lifetime of 595 ps. The spin sensitivity of M-edge XANES allows the 3(d,d) state to be distinguished from a potential 1(d,d) state, as shown by charge transfer multiplet simulations and comparison to triplet nickel(II) oxide. Vibrational cooling of the hot triplet state occurs over tens of ps, with minimal change in the electronic structure of the nickel(II) center. No evidence of an LMCT or MLCT intermediate state is seen within the time resolution of the instrument, suggesting that if such a state exists in NiOEP it depopulates in <25 fs. Finally, this study demonstrates the ability of table high-harmonic XUV sources to measure excited-state spin transitions in molecular transition metal complexes.

Sub-100 Fs Intersystem Crossing to a Metal-Centered Triplet in Ni(II)OEP Observed with M-Edge XANES

2019 ◽  
Author(s):  
Elizabeth S. Ryland ◽  
Kaili Zhang ◽  
Josh Vura-Weis
Keyword(s):  
Excited State ◽  
Time Resolution ◽  
Transient Absorption ◽  
Extreme Ultraviolet ◽  
High Harmonic ◽  
Transient Absorption Spectroscopy ◽  
Intersystem Crossing ◽  
Edge Structure ◽  
State Spin ◽  
X Ray Absorption

Nickel porphyrins have been extenstively studied as photosensitizers due to their long-lived metal-centered excited states. The multiplicity of the (d,d) state, and/or the rate of intersystem crossing between singlet and triplet metal-centered states, has remained uncertain due to the spin-insensitivity of many spectral probes. In this work, we directly probe the metal 3d shell occupation of nickel(II) octaethylporphyrin (NiOEP) using femtosecond M2,3-edge X-ray absorption near-edge structure (XANES). A tabletop high-harmonic source is used to perform 400 nm pump, extreme-ultraviolet probe transient absorption spectroscopy with ~100 fs time resolution. Photoexcitation produces a (π,π*) state that evolves with a time constant of 48 fs to a vibrationally hot metal-centered triplet 3(d,d) excited state with a lifetime of 595 ps. The spin sensitivity of M-edge XANES allows the 3(d,d) state to be distinguished from a potential 1(d,d) state, as shown by charge transfer multiplet simulations and comparison to triplet nickel(II) oxide. Vibrational cooling of the hot triplet state occurs over tens of ps, with minimal change in the electronic structure of the nickel(II) center. No evidence of an LMCT or MLCT intermediate state is seen within the time resolution of the instrument, suggesting that if such a state exists in NiOEP it depopulates in <25 fs. Finally, this study demonstrates the ability of table high-harmonic XUV sources to measure excited-state spin transitions in molecular transition metal complexes.

Excited-State Dynamics in the RNA Nucleotide Uridine 5’-Monophosphate Investigated by Femtosecond Broadband Transient Absorption Spectroscopy

2019 ◽  
Author(s):  
Matthew M. Brister ◽  
Carlos Crespo-Hernández
Keyword(s):  
Excited State ◽  
Excited States ◽  
Ground State ◽  
Transient Absorption ◽  
Electronic Energy ◽  
Transient Absorption Spectroscopy ◽  
Electronic Relaxation ◽  
Vibrationally Excited ◽  
Excited State Dynamics ◽  
Π State

<p></p><p> Damage to RNA from ultraviolet radiation induce chemical modifications to the nucleobases. Unraveling the excited states involved in these reactions is essential, but investigations aimed at understanding the electronic-energy relaxation pathways of the RNA nucleotide uridine 5’-monophosphate (UMP) have not received enough attention. In this Letter, the excited-state dynamics of UMP is investigated in aqueous solution. Excitation at 267 nm results in a trifurcation event that leads to the simultaneous population of the vibrationally-excited ground state, a longlived <sup>1</sup>n<sub>O</sub>π* state, and a receiver triplet state within 200 fs. The receiver state internally convert to the long-lived <sup>3</sup>ππ* state in an ultrafast time scale. The results elucidate the electronic relaxation pathways and clarify earlier transient absorption experiments performed for uracil derivatives in solution. This mechanistic information is important because long-lived nπ* and ππ* excited states of both singlet and triplet multiplicities are thought to lead to the formation of harmful photoproducts.</p><p></p>

scholarly journals Measuring the frequency chirp of extreme-ultraviolet free-electron laser pulses by transient absorption spectroscopy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Thomas Ding ◽  
Marc Rebholz ◽  
Lennart Aufleger ◽  
Maximilian Hartmann ◽  
Veit Stooß ◽  
...  
Keyword(s):  
Free Electron ◽  
Free Electron Laser ◽  
Transient Absorption ◽  
Extreme Ultraviolet ◽  
Ultrashort Pulses ◽  
Laser Pulses ◽  
Transient Absorption Spectroscopy ◽  
Energy Structure ◽  
Frequency Chirp

AbstractHigh-intensity ultrashort pulses at extreme ultraviolet (XUV) and x-ray photon energies, delivered by state-of-the-art free-electron lasers (FELs), are revolutionizing the field of ultrafast spectroscopy. For crossing the next frontiers of research, precise, reliable and practical photonic tools for the spectro-temporal characterization of the pulses are becoming steadily more important. Here, we experimentally demonstrate a technique for the direct measurement of the frequency chirp of extreme-ultraviolet free-electron laser pulses based on fundamental nonlinear optics. It is implemented in XUV-only pump-probe transient-absorption geometry and provides in-situ information on the time-energy structure of FEL pulses. Using a rate-equation model for the time-dependent absorbance changes of an ionized neon target, we show how the frequency chirp can be directly extracted and quantified from measured data. Since the method does not rely on an additional external field, we expect a widespread implementation at FELs benefiting multiple science fields by in-situ on-target measurement and optimization of FEL-pulse properties.

scholarly journals Analytical Theory of Attosecond Transient Absorption Spectroscopy of Perturbatively Dressed Systems

2019 ◽  
Vol 9 (7) ◽  
pp. 1350
Author(s):  
Daria Kolbasova ◽  
Robin Santra
Keyword(s):  
Perturbation Theory ◽  
Absorption Spectroscopy ◽  
Transient Absorption ◽  
Electronic States ◽  
Theoretical Description ◽  
Transient Absorption Spectroscopy ◽  
Electron Dynamics ◽  
Optical Pulses ◽  
Absorption Signal ◽  
Level Model

A theoretical description of attosecond transient absorption spectroscopy for temporally and spatially overlapping XUV and optical pulses is developed, explaining the signals one can obtain in such an experiment. To this end, we employ a two-stage approach based on perturbation theory, which allows us to give an analytical expression for the transient absorption signal. We focus on the situation in which the attosecond XUV pulse is used to create a coherent superposition of electronic states. As we explain, the resulting dynamics can be detected in the spectrum of the transmitted XUV pulse by manipulating the electronic wave packet using a carrier-envelope-phase-stabilized optical dressing pulse. In addition to coherent electron dynamics triggered by the attosecond pulse, the transmitted XUV spectrum encodes information on electronic states made accessible by the optical dressing pulse. We illustrate these concepts through calculations performed for a few-level model.

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